The present invention relates to catheters, cannulae, and the like, and particularly to apparatus that are steerable through body cavities and aimable at obstructions, organs, or tissue within the body from a position external to the body. More particularly, the present invention relates to nitinol tubing for medical devices, including steerable and aimable apparatus.
A great deal of research effort has focused on providing a catheter having a distal end which, when inserted into a body, is readily steerable and aimable to advance the catheter through body cavities and passageways. It has been observed that materials exhibiting mechanical memory properties triggered by heat are particularly useful for enhancing the maneuverability of catheters or like devices. The materials are commonly called "temperature-activated memory materials" or "shape memory alloys" because they move to assume a predetermined shape when heated to a predetermined temperature.
Nitinol, a nickel-titanium alloy, is one such temperature-activated memory material that has been formed into memory element strips and deployed in the distal end of a catheter. Heating the nitinol memory element strips to a given temperature using an electric current provided by a power supply causes the memory elements to deform to assume a predetermined shape, thereby deflecting the distal end of the catheter. See, for example, U.S. Pat. Nos. 4,543,090; 4,601,705; and 4,758,222 for descriptions of known memory element systems for steering and aiming catheters, cannulae, and the like.
Use of shape memory nitinol has previously been used in "strip" or "rod" form in the construction of steerable and aimable apparatus. Such nitinol strips and rods are solid core elements having a circular, rectangular, or other similar cross-sectional shape. In use, these solid core memory element strips or rods are placed on opposing sides of a central lumen formed in an apparatus about the circumference of the apparatus. Selective activation of these memory element strips or rods results in articulation of the apparatus. See, for example, U.S. Pat. No. 4,601,705 for a disclosure of a four-memory element strip steering and aiming system and U.S. Pat. No. 4,758,222 for a disclosure of a steering and aiming system using a spring and one temperature-activated memory element strip.
What is needed is an improved system for steering and aiming an apparatus quickly and effectively without using multiple memory elements or springs. Such an improved steerable and aimable apparatus would, for example, reduce the complexity of the assembly by using fewer pieces.
According to the present invention, a steerable and aimable apparatus includes a flexible, elongated tubular member and a nickel titanium tube. The tubular member has a central axis extending longitudinally therethrough and the nickel titanium tube is formed to include a lumen extending along the central axis. Control means is also provided for selectively heating the nickel titanium tube to move the nickel titanium tube to assume a predetermined shape, thereby moving the tubular member so that it assumes a corresponding predetermined shape.
In one preferred embodiment, the tubular member includes an outer sleeve and an inner sleeve and the nickel titanium tube is sandwiched between the inner and outer sleeves. The inner sleeve is formed to include a through lumen and the control means is operated to heat the nickel titanium tube enough to bend the inner and outer sleeves simultaneously.
In another preferred embodiment, the tubular member includes a cylindrical interior side wall defining a passageway extending longitudinally along the central axis. The nickel titanium tube includes an exterior side wall extending longitudinally along the central axis of the tubular member and engaging the interior side wall of the tubular member. The nickel titanium tube is formed to include a lumen extending along the central axis of the tubular member. Essentially, the main lumen for the apparatus is provided by the nickel titanium tube itself.
Nickel titanium tubing can also be used in pairs to control articulation of a steerable and aimable apparatus in accordance with the present invention. In this embodiment, a pair of nitinol tubes is arranged inside a tubular member in spaced-apart parallel relation on opposite sides of a longitudinally extending lumen. One nitinol tube can be activated to bend the tubular member in a first direction. Alternatively, the other nitinol tube can be activated to bend the tubular member in an opposite second direction,
Advantageously, the improved apparatus is steered and aimed using a nitinol tube instead of solid core nitinol strip or rod. This apparatus is easier to manufacture and assemble.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.